The search for new therapeutic agents has been greatly aided in recent years by a better understanding of the structure of enzymes and other biomolecules associated with diseases. One important class of enzymes that has been the subject of extensive study is protein kinases.
Protein kinases constitute a large family of structurally related enzymes that are responsible for the control of a variety of signal transduction processes within the cell. (See, Hardie, G. and Hanks, S. The Protein Kinase Facts Book, I and II, Academic Press, San Diego, Calif.: 1995). Protein kinases are thought to have evolved from a common ancestral gene due to the conservation of their structure and catalytic function. Almost all kinases contain a similar 250-300 amino acid catalytic domain. The kinases may be categorized into families by the substrates they phosphorylate (e.g., protein-tyrosine, protein-serine/threonine, lipids, etc.). Sequence motifs have been identified that generally correspond to each of these kinase families (See, for example, Hanks, S. K., Hunter, T., FASEB J. 1995, 9, 576-596; Knighton et al., Science 1991, 253, 407-414; Hiles et al., Cell 1992, 70, 419-429; Kunz et al., Cell 1993, 73, 585-596; Garcia-Bustos et al., EMBO J. 1994, 13, 2352-2361).
Many diseases are associated with abnormal cellular responses triggered by protein kinase-mediated events. These diseases include autoimmune diseases, inflammatory diseases, bone diseases, metabolic diseases, neurological and neurodegenerative diseases, cancer, cardiovascular diseases, allergies and asthma, Alzheimer's disease and hormone-related diseases. Accordingly, there has been a substantial effort in medicinal chemistry to find protein kinase inhibitors that are effective as therapeutic agents.
ROCK Protein Kinase
One kinase family of interest is Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK), which is believed to be an effector of Ras-related small GTPase Rho. The ROCK family includes p160ROCK (ROCK-1) (Ishizaki et al., EMBO J. 1996, 15, 1885-1893) and ROKα/Rho-kinase/ROCK-II (Leung et al., J. Biol. Chem. 1995, 270, 29051-29054; Matsui et al., EMBO J. 1996, 15, 2208-2216; Nakagawa et al., FEBS Lett. 1996, 392, 189-193), protein kinase PKN (Amano et al., Science 1996, 271, 648-650; Watanabe et al., Science 1996, 271, 645-648), and citron and citron kinase (Madaule et al. Nature, 1998, 394, 491-494; Madaule et al., FEBS Lett. 1995, 377, 243-248). The ROCK family of kinases have been shown to be involved in a variety of functions including Rho-induced formation of actin stress fibers and focal adhesions (Leung et al., Mol. Cell Biol. 1996, 16, 5313-5327; Amano et al., Science, 1997, 275, 1308-1311; Ishizaki et al., FEBS Lett. 1997, 404, 118-124) and in downregulation of myosin phosphatase (Kimura et al., Science, 1996, 273, 245-248), platelet activation (Klages et al., J. Cell. Biol., 1999, 144, 745-754), aortic smooth muscle contraction by various stimuli (Fu et al., FEBS Lett., 1998, 440, 183-187), thrombin-induced responses of aortic smooth muscle cells (Seasholtz et al., Cir. Res., 1999, 84, 1186-1193), hypertrophy of cardiomyocytes (Kuwahara et al., FEBS Lett., 1999, 452, 314-318), bronchial smooth muscle contraction (Yoshii et al., Am. J. Respir. Cell Mol. Biol., 1999, 20, 1190-1200), smooth muscle contraction and cytoskeletal reorganization of non-muscle cells (Fukata et al., Trends in Pharm. Sci 2001, 22, 32-39), activation of volume-regulated anion channels (Nilius et al., J. Physiol., 1999, 516, 67-74), neurite retraction (Hirose et al., J. Cell. Biol., 1998, 141, 1625-1636), neutrophil chemotaxis (Niggli, FEBS Lett., 1999, 445, 69-72), wound healing (Nobes and Hall, J. Cell. Biol., 1999, 144, 1235-1244), tumor invasion (Itoh et al., Nat. Med., 1999, 5, 221-225) and cell transformation (Sahai et al., Curr. Biol., 1999, 9, 136-145).
More specifically, ROCK has been implicated in various diseases and disorders including hypertension (Satoh et al., J. Clin. Invest. 1994, 94, 1397-1403; Mukai et al., FASEB J. 2001, 15, 1062-1064; Uehata et al., Nature 1997, 389, 990-994; Masumoto et al., Hypertension, 2001, 38, 1307-1310), cerebral vasospasm (Sato et al., Circ. Res. 2000, 87, 195-200; Miyagi et al., J. Neurosurg. 2000, 93, 471-476; Tachibana et al., Acta Neurochir (Wien) 1999, 141, 13-19), coronary vasospasm (Shimokawa et al., Jpn. Cir. J. 2000, 64, 1-12; Kandabashi et al., Circulation 2000, 101, 1319-1323; Katsumata et al., Circulation 1997, 96, 4357-4363; Shimokawa et al., Cardiovasc. Res. 2001, 51, 169-177; Utsunomiya et al., J. Pharmacol. 2001, 134, 1724-1730; Masumoto et al., Circulation 2002, 105, 1545-1547), bronchial asthma (Chiba et al., Comp. Biochem. Physiol. C Pharmacol. Toxicol. Endocrinol. 1995, 11, 351-357; Chiba et al., Br. J. Pharmacol. 1999, 127, 597-600; Chiba et al., Br. J. Pharmacol. 2001, 133, 886-890; lizuka et al., Eur. J. Pharmacol. 2000, 406, 273-279), preterm labor (Niro et al., Biochem. Biophys. Res. Commun. 1997, 230, 356-359; Tahara et al., Endocrinology 2002, 143, 920-929; Kupittayanant et al., Pflugers Arch. 2001, 443, 112-114), erectile dysfunction (Chitaley et al., Nat. Med. 2001, 7, 119-122; Mills et al., J. Appl. Physiol. 2001, 91, 1269-1273), glaucoma (Honjo et al., Arch. Ophthalmol. 2001, 1171-1178; Rao et al., Invest. Ophthalmol. Vis. Sci. 2001, 42, 1029-1037), vascular smooth muscle cell proliferation (Shimokawa et al., Cardiovasc. Res. 2001, 51, 169-177; Morishige et al., Arterioscler. Thromb. Vasc. Biol. 2001, 21, 548-554; Eto et al., Am. J. Physiol. Heart Circ. Physiol. 2000, 278, H1744-H1750; Sawada et al., Circulation 2000, 101, 2030-2023; Shibata et al., Circulation 2001, 103, 284-289), myocardial hypertrophy (Hoshijima et al., J. Biol. Chem. 1998, 273, 7725-77230; Sah et al., J. Biol. Chem. 1996, 271, 31185-31190; Kuwahara et al., FEBS Lett. 1999, 452, 314-318; Yanazume et al., J. Biol. Chem. 2002, 277, 8618-8625), malignoma (Itoh et al., Nat. Med. 1999, 5, 221-225; Genda et al., Hepatology 1999, 30, 1027-1036; Somlyo et al., Biochem. Biophys. Res. Commun. 2000, 269, 652-659), ischemia/reperfusion-induced injury (Ikeda et al., J. of Surgical Res. 2003, 109, 155-160; Miznuma et al. Transplantation 2003, 75, 579-586), endothelial dysfunction (Hernandez-Perera et al., Circ. Res. 2000, 87, 616-622; Laufs et al., J. Biol. Chem. 1998, 273, 24266-24271; Eto et al., Circ. Res. 2001, 89, 583-590), Crohn's Disease and colitis (Segain et al. Gastroenterology 2003, 124(5), 1180-1187), neurite outgrowth (Fournier et al. J. Neurosci. 2003, 23, 1416-1423), Raynaud's Disease (Shimokawa et al. J. Cardiovasc. Pharmacol. 2002, 39, 319-327), angina (Utsunomiya et al. Br. J. Pharmacol. 2001, 134, 1724-1730; Masumoto et al, Circulation 2002, 105, 1545-1547; Shimokawa et al, J. Cardiovasc. Pharmacol., 2002, 40, 751-761; Satoh et al., Jpn. J. Pharmacol., 2001, 87, 34-40), Alzheimer's disease (Zhou et al., Science 2003, 302, 1215-1218), benign prostatic hyperplasia (Rees et al., J. Urology, 2003, 170, 2517-2522), and atherosclerosis (Retzer et al. FEBS Lett. 2000, 466, 70-74; Ishibashi et al. Biochim. Biophys. Acta 2002, 1590, 123-130). Accordingly, the development of inhibitors of ROCK kinase would be useful as therapeutic agents for the treatment of disorders implicated in the ROCK kinase pathway.
ERK Protein Kinase
ERK2 (extracellular signal regulated kinase) is a member of the mammalian mitogen-activated protein (MAP) 1 kinase family. (MAP) 1 kinases are serine/threonine kinases that mediate intracellular signal transduction pathways (Cobb and Goldsmith, J Biol. Chem., 1995, 270, 14843; Davis, Mol. Reprod. Dev. 1995, 42, 459) and are activated by mitogens and growth factors (Bokemeyer et al., Kidney Int. 1996, 49, 1187). Members of the MAP kinase family share sequence similarity and conserved structural domains, and, in addition to ERK2, include the JNK (Jun N-terminal kinase), and p38 kinases. JNKs and p38 kinases are activated in response to the pro-inflammatory cytokines TNF-alpha and interleukin-1, and by cellular stress such as heat shock, hyperosmolarity, ultraviolet radiation, lipopolysaccharides and inhibitors of protein synthesis (Derijard et al., Cell 1994, 76, 1025; Han et al., Science 1994, 265, 808; Raingeaud et al., J Biol. Chem. 1995, 270, 7420; Shapiro and Dinarello, Proc. Natl. Acad. Sci. USA 1995, 92, 12230). In contrast, ERKs are activated by mitogens and growth factors (Bokemeyer et al., Kidney Int. 1996, 49, 1187).
ERK2 is a widely distributed protein kinase that achieves maximum activity when both Thr183 and Tyr185 are phosphorylated by the upstream MAP kinase, MEK1 (Anderson et al., Nature 1990, 343, 651; Crews et al., Science 1992, 258, 478). Upon activation, ERK2 phosphorylates many regulatory proteins, including the protein kinases Rsk90 (Bjorbaek et al., J. Biol. Chem. 1995, 270, 18848) and MAPKAP2 (Rouse et al., Cell 1994, 78, 1027), and transcription factors such as ATF2 (Raingeaud et al., Mol. Cell Biol. 1996, 16, 1247), Elk-1 (Raingeaud et al., Mol. Cell Biol. 1996, 16, 1247), c-Fos (Chen et al., Proc. Natl. Acad. Sci. USA 1993, 90, 10952), and c-Myc (Oliver et al., Proc. Soc. Exp. Biol. Med. 1995, 210, 162). ERK2 is also a downstream target of the Ras/Raf dependent pathways (Moodie et al., Science 1993, 260, 1658) and may help relay the signals from these potentially oncogenic proteins. ERK2 has been shown to play a role in the negative growth control of breast cancer cells (Frey and Mulder, Cancer Res. 1993, 57, 628) and hyperexpression of ERK2 in human breast cancer has been reported (Sivaraman et al., J Clin. Invest. 1997, 99, 1478). Activated ERK2 has also been implicated in the proliferation of endothelin-stimulated airway smooth muscle cells, suggesting a role for this kinase in asthma (Whelchel et al., Am. J. Respir. Cell Mol. Biol. 1997, 16, 589).
GSK-3 Protein Kinase
Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase comprised of α and β isoforms that are each encoded by distinct genes [Coghlan et al., Chemistry & Biology 2000, 7, 793-803; and Kim and Kimmel, Curr. Opinion Genetics Dev., 2000 10, 508-514]. GSK-3 has been implicated in various diseases including diabetes, Alzheimer's disease, CNS disorders such as manic depressive disorder and neurodegenerative diseases, and cardiomyocyte hypertrophy [PCT Application Nos.: WO 99/65897 and WO 00/38675; and Haq et al., J. Cell Biol. 2000, 151, 117-130]. These diseases are associated with the abnormal operation of certain cell signaling pathways in which GSK-3 plays a role. GSK-3 has been found to phosphorylate and modulate the activity of a number of regulatory proteins. These proteins include glycogen synthase, which is the rate limiting enzyme necessary for glycogen synthesis, the microtubule associated protein Tau, the gene transcription factor β-catenin, the translation initiation factor e1F2B, as well as ATP citrate lyase, axin, heat shock factor-1, c-Jun, c-myc, c-myb, CREB, and CEPBα. These diverse protein targets implicate GSK-3 in many aspects of cellular metabolism, proliferation, differentiation, and development.
In a GSK-3 mediated pathway that is relevant for the treatment of type II diabetes, insulin-induced signaling leads to cellular glucose uptake and glycogen synthesis. Along this pathway, GSK-3 is a negative regulator of the insulin-induced signal. Normally, the presence of insulin causes inhibition of GSK-3 mediated phosphorylation and deactivation of glycogen synthase. The inhibition of GSK-3 leads to increased glycogen synthesis and glucose uptake [Klein et al., PNAS 1996, 93, 8455-8459; Cross et al., Biochem. J. 1994, 303, 21-26); Cohen, Biochem. Soc. Trans. 1993, 21, 555-567; and Massillon et al., Biochem J. 1994, 299, 123-128]. However, in a diabetic patient, where the insulin response is impaired, glycogen synthesis and glucose uptake fail to increase despite the presence of relatively high blood levels of insulin. This leads to abnormally high blood levels of glucose with acute and long-term effects that may ultimately result in cardiovascular disease, renal failure and blindness. In such patients, the normal insulin-induced inhibition of GSK-3 fails to occur. It has also been reported that in patients with type II diabetes, GSK-3 is overexpressed [see, PCT Application: WO 00/38675]. Therapeutic inhibitors of GSK-3 are therefore potentially useful for treating diabetic patients suffering from an impaired response to insulin.
GSK-3 activity is also associated with Alzheimer's disease. This disease is characterized by the well-known β-amyloid peptide and the formation of intracellular neurofibrillary tangles. Aβ peptides are derived from the amyloid precursor protein (APP) by sequential proteolysis, catalysed by the aspartyl protease BACE2, followed by presenilin-dependent γ-secretase cleavage. It has been demonstrated that antibodies against β-amyloid plaques can slow cognitive decline in patients with Alzheimer's disease (Hock et al., Neuron, 2003, 38, 547-554), and thus other β-amyloid-lowering strategies (e.g., the development of agents capable of inhibiting β-amyloid peptide) would be useful in the treatment of Alzherimer's disease and other psychotic and neurodegenerative disorders. Additionally, the neurofibrillary tangles contain hyperphosphorylated Tau protein, in which Tau is phosphorylated on abnormal sites, and thus agents capble of inhibiting the hyperphosphorylation of Tau protein would be useful in the treatment of Alzherimer's disease and other psychotic and neurodegenerative disorders.
GSK-3 is known to phosphorylate these abnormal sites in cell and animal models. Furthermore, inhibition of GSK-3 has been shown to prevent hyperphosphorylation of Tau in cells [Lovestone et al., Current Biology 1994, 4, 1077-86; and Brownlees et al., Neuroreport 1997, 8, 3251-55]. Therefore, GSK-3 activity promotes generation of the neurofibrillary tangles and the progression of Alzheimer's disease. It has also been shown that GSK-3 facilitates APP processing and that a GSK-3 inhibitor (lithium) inhibits of the generation of Aβ peptides through the inhibition of GSK-3 (Phiel et al. Nature 2003, 423, 435-439). Thus, the development of inhibitors of GSK-3 would be useful for the reduction of the formation of amyloid plaques and neurofibrillry tangles, the pathological hallmarks of Alzheimer's Disease, and would also be useful for the treatment of other psychotic and neurodegenerative disorders.
Another substrate of GSK-3 is β-catenin, which is degradated after phosphorylation by GSK-3. Reduced levels of β-catenin have been reported in schizophrenic patients and have also been associated with other diseases related to increase in neuronal cell death [Zhong et al., Nature 1998, 395, 698-702; Takashima et al., PNAS 1993, 90, 7789-93; and Pei et al., J. Neuropathol. Exp 1997, 56, 70-78].
GSK-3 activity is also associated with stroke [Wang et al., Brain Res 2000, 859, 381-5; Sasaki et al., Neurol Res 2001, 23, 588-92; Hashimoto et al., J. Biol. Chem 2002, 277, 32985-32991].
AGC-Family of Protein Kinases
The AGC sub-family of kinases phosphorylate their substrates at serine and threonine residues and participate in a variety of well-known signaling processes, including, but not limited to cyclic AMP signaling, the response to insulin, apoptosis protection, diacylglycerol signaling, and control of protein translation (Peterson et al., Curr. Biol. 1999, 9, R521). This sub-family includes PKA, PKB (c-Akt), PKC, PRK1, 2, p70S6K, SGK1, and PDK.
AKT Protein Kinase
AKT (also known as PKB or Rac-PK beta), a serine/threonine protein kinase, has been shown to be overexpressed in several types of cancer and is a mediator of normal cell functions [(Khwaja, A., Nature 1999, 401, 33-34); (Yuan, Z. Q., et al., Oncogene 2000, 19, 2324-2330); (Namikawa, K., et al., J Neurosci. 2000, 20, 2875-2886,)]. AKT comprises an N-terminal pleckstrin homology (PH) domain, a kinase domain and a C-terminal “tail” region. Three isoforms of human AKT kinase (AKT-1, -2 and -3) have been reported so far [(Cheng, J. Q., Proc. Natl. Acad. Sci. USA 1992, 89, 9267-9271); (Brodbeck, D. et al., J. Biol. Chem. 1999, 274, 9133-9136)]. The PH domain binds 3-phosphoinositides, which are synthesized by phosphatidyl inositol 3-kinase (PI3K) upon stimulation by growth factors such as platelet derived growth factor (PDGF), nerve growth factor (NGF) and insulin-like growth factor (IGF-1) [(Kulik et al., Mol. Cell. Biol., 1997, 17, 1595-1606,); (Hemmings, B. A., Science, 1997, 275, 628-630)]. Lipid binding to the PH domain promotes translocation of AKT to the plasma membrane and facilitates phosphorylation by another PH-domain-containing protein kinases, PDK1 at Thr308, Thr309, and Thr305 for the AKT isoforms 1, 2 and 3, respectively. A second, as of yet unknown, kinase is required for the phosphorylation of Ser473, Ser474 or Ser472 in the C-terminal tails of AKT-1, -2 and -3 respectively, in order to yield a fully activated AKT enzyme.
Once localized to the membrane, AKT mediates several functions within the cell including the metabolic effects of insulin (Calera, M. R. et al., J. Biol. Chem. 1998, 273, 7201-7204) induction of differentiation and/or proliferation, protein synthesis and stress responses (Alessi, D. R. et al., Curr. Opin. Genet. Dev. 1998, 8, 55-62,).
Manifestations of altered AKT regulation appear in both injury and disease, the most important role being in cancer. The first account of AKT was in association with human ovarian carcinomas where expression of AKT was found to be amplified in 15% of cases (Cheng, J. Q. et al., Proc. Natl. Acad. Sci. U.S.A. 1992, 89, 9267-9271). It has also been found to be overexpressed in 12% of pancreatic cancers (Cheng, J. Q. et al., Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 3636-3641). It was demonstrated that AKT-2 was over-expressed in 12% of ovarian carcinomas and that amplification of AKT was especially frequent in 50% of undifferentiated tumours, suggesting that AKT may also be associated with tumour aggressiveness (Bellacosa, et al., Int. J. Cancer 1995, 64, 280-285).
Increased levels of PI3K pathway activity has been directly associated with the development of a number of human cancers, progression to an aggressive refractory state (acquired resistance to chemotherapies) and poor prognosis. This increased activity has been attributed to a series of key events including decreased activity of negative pathway regulators such as the phosphatase PTEN, activating mutations of positive pathway regulators such as Ras, and overexpression of components of the pathway itself such as AKT, examples include: brain (gliomas), breast, colon, head and neck, kidney, lung, liver, melanoma, ovarian, pancreatic, prostate, sarcoma, thyroid [(Teng, D. H. et al., Cancer Res., 1997 57, 5221-5225), (Brognard, J. et al., Cancer Res., 2001, 61, 3986-3997), (Cheng, J. Q. et al., Proc. Natl. Acad. Sci. 1996, 93, 3636-3641), (Int. J. Cancer 1995, 64, 280), (Graff, J. R., Expert Opin. Ther. Targets 2002, 6, 103-113), (Am. J. Pathol. 2001, 159, 431)].
Additionally, decreased pathway function through gene knockout, gene knockdown, dominant negative studies, and small molecule inhibitors of the pathway have been demonstrated to reverse many of the cancer phenotypes in vitro (some studies have also demonstrated a similar effect in vivo) such as block proliferation, reduce viability and sensitize cancer cells to known chemotherapies in a series of cell lines, representing the following cancers: pancreatic [(Cheng, J. Q. et al., Proc. Natl. Acad. Sci. 1996, 93, 3636-3641), (Neoplasia 2001, 3, 278)], lung [(Brognard, J. et al., Cancer Res. 2001, 61, 3986-3997), (Neoplasia 2001, 3, 278)], ovarian [(Hayakawa, J. et al., Cancer Res. 2000, 60, 5988-5994), (Neoplasia 2001, 3, 278)], breast (Mol. Cancer Ther. 2002, 1, 707), colon [(Neoplasia 2001, 3, 278), (Arico, S. et al., J. Biol. Chem. 2002, 277, 27613-27621)], cervical (Neoplasia 2001, 3, 278), prostate [(Endocrinology 2001, 142, 4795), (Thakkar, H. et al. J. Biol. Chem. 2001, 276, 38361-38369), (Chen, X. et al., Oncogene 2001, 20, 6073-6083)] and brain (glioblastomas) [(Flynn, P. et al., Curr. Biol. 2000, 10, 1439-1442)].
PKA Protein Kinase
PKA (also known as cAMP-dependent protein kinase) has been shown to regulate many vital functions including energy metabolism, gene transcription, proliferation, differentiation, reproductive function, secretion, neuronal activity, memory, contractility and motility (Beebe, S. J., Semin. Cancer Biol. 1994, 5, 285-294). PKA is a tetrameric holoenzyme, which contains two catalytic subunits bound to a homo-dimeric regulatory subunit (which acts to inhibit the catalytic sub-units). On binding of cAMP (enzyme activation), the catalytic subunits dissociate from the regulatory subunits to yield the active serine/threonine kinase (McKnight, G. S. et al., Recent Prog. Horm. Res. 1988, 44, pp. 307). Three isoforms of the catalytic subunit (C-α, C-β and C-γ) have been reported to date (Beebe, S. J. et al., J. Biol. Chem. 1992, 267, 25505-25512) with the C-α subunit being the most extensively studied, primarily because of its elevated expression in primary and metastatic melanomas (Becker, D. et al., Oncogene 1990, 5, 1133). To date, strategies to modulate the activity of the C-α subunit involve the use of antibodies, molecules that block PKA activity by targeting regulatory dimers and antisense oligonucleotides expression.
P70S6K Protein Kinase
The ribosomal protein kinases p70S6K-1 and -2 are also members of the AGC sub-family of protein kinases and catalyze the phosphorylation and subsequent activation of the ribosomal protein S6, which has been implicated in the translational up-regulation of mRNAs coding for the components of the protein synthetic apparatus. These mRNAs contain an oligopyrimidine tract at their 5′ transcriptional start site, termed a 5′TOP, which has been shown to be essential for their regulation at the translational level (Volarevic, S. et al., Prog. Nucleic Acid Res. Mol. Biol. 2001, 65, 101-186). p70S6K dependent S6 phosphorylation is stimulated in response to a variety of hormones and growth factors primarily via the PI3K pathway (Coffer, P. J. et al., Biochem. Biophys. Res. Commun, 1994 198, 780-786), which may be under the regulation of mTOR, since rapamycin acts to inhibit p70S6K activity and blocks protein synthesis, specifically as a result of a down-regulation of translation of these mRNA's encoding ribosomal proteins (Kuo, C. J. et al., Nature 1992, 358, 70-73).
SGK1 Protein Kinase
Serum- and glucocorticoid-induced protein kinase 1 (SGK1) is an ubiquitously expressed kinase. SGK1, together with the related kinases serum- and glucocorticoid-induced protein kinase 2 (SGK2) and serum- and glucocorticoid-induced protein kinase (SGK3), belongs to the AGC subfamily of protein kinases. The catalytic domain of SGK1 is 54% identical to that of Protein Kinase B (PKB also known as AKT) (Lang, F. and Cohen, P. Sci STKE. 2001 Nov. 13; 2001(108):RE17).
SGK1 is important for regulating Na+ homeostasis. It affects Na+ resorbtion by the amelioride-sensitive epithelial Na+ channels (ENaC) located in the distal renal tubal cells (Pearce D Trends Endocrinol Metab (2001) 12: 341-347). SGK1-deficient mice have decreased renal Na+ excretion during Na+ depletion (Wullf, P. et al. J Clin Invest (2002) 110:1263-1268) and its activity is relevant to hypertension in man (Busjahn, A. et al. Hypertension (2002) 40:256-260). SGK1 regulation of ENaC may also affect cell volume Bohmer, C., et al., Cell Physiol Biochem. (2000) 10:187-194).
SGK1 has a potential role in regulating cell survival through its phosphorylation of FKHRL1, a transcription factor involved in controlling apoptosis (Brunet, A. et al. Mol Cell Biol (2001) 21:952-65). It is also involved in regulation of potassium ion channels (Gamper N., et al. Pflugers Arch (2002) 445:60-66) and thus plays a role in cell survival and neuronal excitability.
PDK1 Protein Kinase
In vitro PDK1 catalyses the phosphorylation of Thr252 in the activation loop of the p70 catalytic domain, which is indispensable for p70 activity (Alessi, D. R., Curr. Biol., 1998, 8, 69-81). The use of rapamycin and gene deletion studies of dp70S6K from Drosophila and p70S6K1 from mouse have established the central role p70 plays in both cell growth and proliferation signaling.
The 3-phosphoinositide-dependent protein kinase-1 (PDK1) plays a key role in regulating the activity of a number of kinases belonging to the AGC subfamily of protein kinases (Alessi, D. et al., Biochem. Soc. Trans 2001, 29, 1). These include isoforms of protein kinase B (PKB, also known as AKT), p70 ribosomal S6 kinase (S6K) (Avruch, J. et al., Prog. Mol. Subcell. Biol. 2001, 26, 115), and p90 ribosomal S6 kinase (Frödin, M. et al., EMBO J. 2000, 19, 2924-2934). PDK1 mediated signaling is activated in response to insulin and growth factors and as a consequence of attachment of the cell to the extracellular matrix (integrin signaling). Once activated these enzymes mediate many diverse cellular events by phosphorylating key regulatory proteins that play important roles controlling processes such as cell survival, growth, proliferation and glucose regulation [(Lawlor, M. A. et al., J. Cell Sci. 2001, 114, 2903-2910), (Lawlor, M. A. et al., EMBO J. 2002, 21, 3728-3738)]. PDK1 is a 556 amino acid protein, with an N-terminal catalytic domain and a C-terminal pleckstrin homology (PH) domain, which activates its substrates by phosphorylating these kinases at their activation loop (Belham, C. et al., Curr. Biol. 1999, 9, R93-R96). Many human cancers including prostate and NSCL have elevated PDK1 signaling pathway function resulting from a number of distinct genetic events such as PTEN mutations or over-expression of certain key regulatory proteins [(Graff, J. R., Expert Opin. Ther. Targets 2002, 6, 103-113), (Brognard, J., et al., Cancer Res. 2001, 61, 3986-3997)]. Inhibition of PDK1 as a potential mechanism to treat cancer was demonstrated by transfection of a PTEN negative human cancer cell line (U87MG) with antisense oligonucleotides directed against PDK1. The resulting decrease in PDK1 protein levels led to a reduction in cellular proliferation and survival (Flynn, P., et al., Curr. Biol. 2000, 10, 1439-1442). Consequently the design of ATP binding site inhibitors of PDK1 offers, amongst other treatments, an attractive target for cancer chemotherapy.
The diverse range of cancer cell genotypes has been attributed to the manifestation of the following six essential alterations in cell physiology: self-sufficiency in growth signaling, evasion of apoptosis, insensitivity to growth-inhibitory signaling, limitless replicative potential, sustained angiogenesis, and tissue invasion leading to metastasis (Hanahan, D. et al., Cell 2000, 100, 57-70). PDK1 is a critical mediator of the PI3K signalling pathway, which regulates a multitude of cellular function including growth, proliferation and survival. Consequently, inhibition of this pathway could affect four or more of the six defining requirements for cancer progression. As such it is anticipated that a PDK1 inhibitor will have an effect on the growth of a very wide range of human cancers.
Accordingly, there is a great need to develop inhibitors of ROCK, ERK, GSK, and members of the AGC sub-family of protein kinases (e.g., PKA, PDK, p70S6K-1 and -2, and AKT) that would be useful in treating various diseases or conditions associated with ROCK, ERK or GSK activation, or activation of the AGC sub-family of protein kinases (e.g., PKA, PDK, p70S6K-1 and -2, and AKT), particularly given the inadequate treatments currently available for the majority of these disorders.